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Chapter 12

The History of Life

relative dating a method of determining whether an event or object, such as a fossil, is older or younger than other events without referring to the object's age in years
radiometric dating a method of determining the absolute age of an object, often by comparing the relative percentages of a radioactive (parent) isotope and a stable (daughter) isotope
isotope an atom that has the same number of protons (or the same atomic number) as other atoms of the same element do but that has a different number of neutrons (and thus a different atomic mass)
half-life the time required for half of a sample of a radioactive isotope to break down by radioactive decay to form a daughter isotope
index fossil a fossil that is used to establish the age of a rock layer because the fossil is distinct, abundant, and widespread and the species that formed that fossil existed for only a short span of geologic time
geologic time scale a standard method used to divide Earth's long natural history into manageable parts
era unit of geologic time that includes two or more periods
period unit of geologic time that lasts tens of millions of years and is associated with a particular type of rock system
epoch smallest unit of geologic time, lasting several million years
nebula large cloud of gas and dust in interstellar space; a region in space where stars are born
ribozyme a type of RNA that can act as an enzyme
cyanobacteria bacteria that can carry out photosynthesis
endosymbiosis a mutually beneficial relationship in which one organism lives within another
Paleozoic era of geologic time (from 544 to 248 million years ago) during which members of every major animal group alive today evolved
Cambrian explosion earliest part of the Paleozoic era, when a huge diversity of animal species evolved
Mesozoic era during which dinosaurs roamed Earth (from 248 million years ago to 65 million years ago)
Cenozoic geologic time period that began 65 million years ago and still continues today
primate a member of the order Primates, the group of mammals that includes humans, apes, monkeys, and prosimians; typically distinguished by a highly developed brain, forward-directed eyes and binocular
prosimian oldest primate group that includes mostly small, nocturnal primates such as lemurs
anthropoid human-like primate
hominid a member of the family Hominidae of the order Primates; characterized by bipedalism, relatively long lower limb, and lack of tail; examples include humans and their ancestors
bipedal animal that walks on two legs
Created by: kaseywallace